Paul, welcome to the forums. I'm sorry to hear that your family is dealing with this.

Postpartum preeclampsia and eclampsia are treated the same as when they occur before delivery, which usually means IV magnesium sulfate to lower the risk of more seizures, blood pressure medication to drop pressures postpartum (there are questions about it before delivery, but afterwards it just depends on how high her pressures are), and sometimes diuretics to help mobilize the fluid. I would want her to be seen by a maternal-fetal medicine specialist working in hypertensive pregnancies. In your shoes I'd contact APEC at http://www.apec.org.uk/ because they can put you in touch with a local specialist quickly.

My wife was admitted to hospital 10 days post birth of twin girls suffering from a severe headache. Started vomiting on way to hospital. 3 hours after arriving at hospital had 1st seizure with second one 5 hours later.
Was given magnesium sulphate and remained in intensive care for 9 days. She also developed a blood clot on left lung which was thankfully picked up early and is taking wolfarin.
Since moved to another hospital where for the last 4 days (plus 4 days in intensive care) she is experience very bad headaches (albeit not to the same scale when admitted). The headaches is linked in with raised BP (circa 145-160 / 80-100) as well as vomiting.
She takes the following medication:
Thyroxine, calcium tablets, alphacalcidol for a Thyroid Condition; Wolfarin for the Blood Clot; and various headache relief tablets which do not necessarily work; and occasionaly some BP tablets.
Can anyone help or advise how long this can go on for, whom she should be under (obstetrician or neurologist or other) and what is the best medication she should be taking.
Many thanks
Paul (Husband)